This invention relates to a method of warming up a fixing device in an image formation apparatus such as a printer, a facsimile, or a copier for forming an image using electrophotography, an image formation apparatus using the method and a method of determining a humidly value used in the image formation apparatus.
Generally, an image formation apparatus using electrophotography includes a photoconductor having a photosensitive layer on an outer peripheral surface thereof, a charging member for uniformly charging the outer peripheral surface of the photoconductor, a light exposure member for selectively exposing the outer peripheral surface uniformly charged by the charging member to light for forming an electrostatic latent image, a developing member for providing toner as a developer to the electrostatic latent image formed by the light exposure member for producing a visible image (toner image), a transfer member for transferring the toner image developed by the developing member to a paper as a transfer target, and a fuser for fixing the toner image onto the paper to which the toner image has been transferred by the transfer member.
Known as an image formation apparatus in a related art is an image formation apparatus including a temperature sensor and a humidity sensor for determining a transfer voltage in response to the temperature and the humidity detected by the sensors. (For example, refer to JP-A-2000-039780 (paragraph and FIG. 1)).
A fuser in a related art has at least two fixing members for forming a fixing nip part. For example, one fixing member is implemented as a fixing roller (or a fixing belt) which has a heating member and is rotated, and the other is implemented as a pressurization member (for example, a pressurization roller) pressed against the one fixing member for rotation (see, JP-A-2000-214723, JP-A-2002-258652 and JP-A-2001-134132, for example).
When the image formation apparatus performs an image formation operation, a warm-up operation of the fuser is performed. The warm-up operation is performed until the fixing roller, etc., reaches a predetermined temperature as the heating member heats the fixing roller, etc., and the pressurization member while the fixing roller, etc., and the pressurization member are rotated. The pressurization member is heated by heat conduction from the fixing roller, etc.
Generally, when the power is turned on, the fuser is warmed up; if no print signal is input for a predetermined time, a standby state is entered for power saving and later when a print signal is input, the fuser is warmed up.
After the completion of the warm-up operation, the record medium, on which the toner image is formed, is passed through the nip part, whereby the toner is fused on the paper.
Generally, PI-based or silicon-based material used with an electric insulation layer or an adhesive layer of the fixing roller and the pressurization member and so on has a water absorption property. Thus, if it is let alone for a long time in a high-humidity environment in the rainy season, etc., the fixing roller absorbs water content. If the temperature of the fixing roller rapidly is risen in a state that the fixing roller has the water content, the water content in the electric insulation layer and the adhesive layer is vaporized and expanded in a stroke and a heat element and the electric insulation layer are pushed up from a core. Accordingly, adhesion of the heat element, the electric insulation layer, and the core are completely broken and peels. If the constitution of the adhesive layer is thus broken and the heat element and the electric insulation layer float, the heat conduction from the heat element to the core is hindered and thus local heating of the heat element occurs, etc., causing a failure to occur.
The following fuser is known as a fuser in a related art: a humidity detection member is provided in the proximity of a fixing roller in apparatus and the temperature increase rate of the fixing roller is changed in response to the humidity condition in the apparatus just after power is turned on, namely, if the humidity in the apparatus is higher than a reference value, the water absorption state in an electric insulation layer and an adhesive layer is determined to be high, and the temperature increase rate of the fixing roller is decreased for evaporating the water content in the electric insulation layer and the adhesive layer gradually over a period of time, thereby preventing trouble caused by destruction of the electric insulation layer caused by rapid vaporization and expansion (For example, refer to JP-A-2000-214723).
In the image formation apparatus described in JP-A-2000-214723, a transfer member is housed in the apparatus and thus it is appropriate to place the humidity sensor for controlling the transfer voltage in the apparatus and control the image formation apparatus (transfer voltage) based on the humidity value provided any time by the humidity sensor.
On the other hand, in the image formation apparatus, it may be undesirable to control the image formation apparatus based on the humidity value provided any time by the humidity sensor placed in the apparatus.
For example, if paper supplied to the image formation apparatus is set in the image formation apparatus from the state in which the paper is placed outside the apparatus or is previously set in the image formation apparatus, usually the set position is a position easily affected by the environment outside the apparatus. In such a case, it is undesirable to perform control concerning paper based on the humidity value provided any time by the humidity sensor placed in the apparatus, because when the image formation apparatus operates, the internal humidity gradually differs from the environmental moisture (usually, goes lower than the environmental moisture).